This application is based on application No. MI98A 0001023 filed in Italy, the content of which is incorporated hereinto by reference.
The present invention relates to an IR- and UV-radiation-sensitive Composition and to a lithographic plate.
In particular, the invention relates to an IR- and UV-radiation-sensitive composition which is useful for producing a positive-type lithographic plate.
As is known, the technique of printing using a lithographic plate is based on the distinct partition fatty substances and water. The fatty substance or ink is preferably retained by the image area and the water is preferably retained by the non-image area. When the surface of a suitably prepared lithographic plate is moistened with water and then coated with ink, the non-image area retains the water and repels the ink, while the image area accepts the ink and repels the water. Then, the ink on the image area is transferred onto the surface of a material on which it is desired to reproduce the image, such as, for example, card, fabric and the like.
In general, the lithographic plates used in printing processes are formed of an aluminium support coated with a light-sensitive (photosensitive) composition. When this composition reacts to light of a suitable wavelength, such that the portion exposed to the light becomes soluble and thus able to be removed during the developing process, the printing process is referred to as a xe2x80x9cpositivexe2x80x9d process. In contrast, when the portion exposed to the light becomes insoluble, the printing process is referred to as a xe2x80x9cnegativexe2x80x9d process. In both cases, the remaining image area is lipophilic and thus accepts the ink, whereas the non-image area is hydrophilic and accepts the water.
Recent developments in the field of lithographic plates are oriented towards the search for compositions that are sensitive to laser light, preferably in the near-IR region, in particular to a laser light controlled by software, so as to transfer the image created by computer directly onto the surface of the plate. This technique has the advantage of dispensing with photographic films, with a consequent reduction in the pollution resulting from the chemical substances used to prepare and produce these films, and elimination of all the problems encountered in transferring the image onto the plate via photographic films.
Firstly, a composition which is sensitive to IR radiation emitted by a laser might make the system more reliable.
Secondly, it would be possible to work in ambient light, thus dispensing with the need for automatic loading systems and darkrooms.
Patent application WO 96/20429 describes a method for forming a lithographic printing matrix by means of the heat-printing method. This method includes the following stages: (i) coating a support, which can be used as a lithographic support, with a positive-type photosensitive composition comprising a naphthoquinonediazide ester of a phenolic resin or a naphthoquinonediazide ester and a phenolic resin and at least one substance capable of absorbing in the IR region, (ii) exposing the system to ultraviolet light (UV) so as to enable the photosensitive composition to be developed, (iii) imprinting on the plate with IR radiation emitted by a laser, and (iv) developing the plate in order to remove those areas of the photosensitive composition that have not been exposed to the laser.
In addition, in the course of the description, it is stated that the combination of the stages of exposure to light (UV) and of heating (by IR radiation) is essential for forming the image (page 7, lines 1-3).
Patent application WO 97/39894 describes a heat-sensitive olefinic composition comprising a polymer substance which is soluble in aqueous developer and a compound which reduces the solubility of the polymer substance in aqueous developer, characterized in that the solubility of the composition in aqueous developer is increased by heating but is not increased by the incident UV radiation (see Claim 1). In other words, the said plate is sensitive to IR but not to UV.
Preferably, the heat-sensitive composition comprises no UV-sensitive components (page 17, lines 17-18).
EP-A-0 833 204 discloses an infrared radiation sensitive imaging composition contains two essential component, namely an infrared radiation absorbing material, and a phenolic resin that is either mixed or reacted with an o-diazonaphthoquinone derivative. These compositions are useful in imaging elements such as lithographic printing plates that can be used to provide either positive or negative images using laser imaging, and that can be adapted to direct-to-plate imaging procedures. However, none of the examples of EP-A-0 833 204 relates to the use of said composition in a process for obtaining an image after UV exposure only.
Photosensitive plates which, like those of the abovementioned patent applications WO 96/20429 and WO 97/39894, necessarily require exposure to IR light, are currently seldom used since plants capable of printing on a lithographic plate with laser light are still very expensive. Thus, a period of transition is currently being experienced during which many operators are still using the old technique of printing on the plate by exposure to UV lamps by means of a master image, while a fewxe2x80x94those who already have the necessary equipmentxe2x80x94require plates that are sensitive to IR light.
Patent application EP 0 672 954 attempts to address this requirement, disclosing a photosensitive coating for a lithographic plate which is sensitive to both UV and IR radiation and is capable of functioning in both positive and negative modes. The said coating includes a resol resin, a novolac resin, an s-triazine substituted with a haloalkyl group and an IR absorber. The solubility of the abovementioned composition in a solution of alkaline aqueous developer is reduced in the exposed area and increased in the unexposed area during the stages of (i) exposure to the radiation which forms the image, and (ii) heating. In the course of the description, it is specified that in order to be able to use the plate in negative mode, it is essential that both resol and novolac resins are present (page 4, lines 10-13).
The inventors of the present invention have used a plate according to patent application EP 0 672 954 to form UV-positive images and have found that the image thus obtained shows little resistance either to the alkaline developer solution or to the isopropyl alcohol in the bathing solution used during the printing, and in addition the said image also shows little resistance to mechanical abrasion.
A first object of the present invention is to provide a composition which is sensitive to both IR and UV radiation.
A second object of the present invention is that the said composition should give good results during alkaline developing, irrespective of the system (UV or IR) used to imprint it.
A third object of the present invention is that the said composition should give an image which, after developing, has good resistance to the solvents used in printing processes and, in particular, to isopropyl alcohol.
A fourth object of the present invention is to provide a lithographic plate comprising a composition having the abovementioned characteristics.
The term xe2x80x9clithographic platexe2x80x9d is understood to refer to a support coated with a photosensitive coating which, after having been appropriately exposed and developed, is used as a planographic matrix in printing processes in which there is a distinct partition fatty substances and water.
Typical examples of support materials are aluminium, zinc and copper, polymeric supports such as polyester, and paper coated with a polymer.
Even more typically, the support is a metal sheet, made of electrograined aluminium, which has been oxidized and suitably treated to receive the photosensitive composition.
The term xe2x80x9cpositive typexe2x80x9d is understood to mean that that portion of photosensitive coating exposed to the radiation becomes soluble so that it can be removed during the process for developing the plate. Typically, the developing process is carried out in alkali with a conductivity of 75 and 110 mS.
The term xe2x80x9cdiazo resinxe2x80x9d is understood to refer to the product of esterification of a 2,1-naphthoquinonediazide-4-sulphonyl chloride with a product of polycondensation of phenol or homologues thereof such as, for example, m-cresol or symmetric xylenol. Typical examples of such commercial diazo resins are the products RO 874 and RO 849 from the company Rohner (Pratteln, Basle, Switzerland) and A 938 from the company Materiali Sensibili (Milan, Italy).
Alternatively, the term xe2x80x9cdiazo resinxe2x80x9d is understood to refer to the product of esterification of a 2,1-naphthoquinonediazide-5-sulphonyl chloride with a product of polycondensation of phenol or homologues thereof such as, for example, m-cresol and symmetric xylenol. Typical examples of such commercial diazo resins are the products PW 1160 and PW 1161 from the company Clariant (Wiesbaden, Germany) and DRS 25 from the company Materiali Sensibili.
In general, the diazo resin has a weight-average molecular weight of 5000 and 12,000.
The term xe2x80x9cnovolacxe2x80x9d is understood to refer to a polymer obtained, in acid medium, by reaction formaldehyde and phenol and/or m-cresol and/or symmetric xylenol in a molar ratio of less than 1 (for example, formaldehyde: phenol=1:2).
Typical examples of commercial novolac resins are high weight-average molecular weight novolac resin such as LB 6564 (weight-average molecular weight=6000-10,000) and LB 744 (weight-average molecular weight=8000-13,000) from the company Bakelite (Germany), R 7100 (weight-average molecular weight=8000-10,000) from the company Rohner, and PN 430 (weight-average molecular weight=5000-9500) from the company Clariant and low weight-average molecular weight novolac resin such as PN 320 (weight-average molecular weight=3000-5000). A preferred form of R 7100 is obtained by removing monomers from LB 744, thus resulting in a substantially monomers-free resin having a weight-average molecular weight of from 9,500 to 10,500.
The term xe2x80x9cdiazo esterxe2x80x9d is understood to refer to the product of total or partial esterification of a 2,1-naphthoquinonediazidesulphonyl chloride with a tetrahydroxybenzophenone.
Typical examples of diazo esters are those obtained by total or partial esterification of a 2,3,4,4xe2x80x2-tetrahydroxybenzophenone or a 2,2xe2x80x2,4,4xe2x80x2-tetrahydroxybenzophenone with 2,1-naphthoquinonediazide-4-sulphonyl chloride or those obtained by total or partial esterification of a 2,3,4,4xe2x80x2-tetrahydroxybenzophenone or of a 2,2xe2x80x2,4,4xe2x80x2-tetrahydroxybenzophenone with 2,1-naphthoquinonediazide-5-sulphonyl chloride.
A typical example of a diazo ester is the product obtained by total or partial esterification of 2,2xe2x80x2,4,4xe2x80x2-tetrahydroxybenzophenone with 2,1-naphthoquinonediazide-4-sulphonyl chloride giving a mixture of mono-, di-, tri- and tetra ester of 2,2xe2x80x2,4,4xe2x80x2-tetrahydroxybenzophenone, which is sold under the name SDBZ by the company Materiali Sensibili. Typically, SDBZ contains from 5 to 20% of monoester, from 40 to 60% of diester, from 20 to 40% of triester and from 1 to 10% of tetraester of 2,2xe2x80x2,4,4xe2x80x2-tetrahydroxybenzophenone.
The term xe2x80x9cabsorberxe2x80x9d is understood to refer to a substance capable of absorbing radiation of a certain wavelength. Preferably, the absorber is soluble in water, ketones and/or glycols, alcohols and/or mixtures thereof.
Typical examples of absorbers are the commercial products KF 646, KF 645, KF 810, KF 1003, KF 1002, IR HBB 812 and KF 818 from the company Riedel-de-Haen/Allied Signal (Seelze, Germany), the commercial products ADS 805PI, ADS805PP, ADS805PA, ADS805PF, ADS812MI, ADS812MI, ADS815EI, ADS818HI, ADS818HT, ADS822MT, ADS830AT, ADS 830A and ADS838MT from the company American Dye Source (Varennes, Quebec, Canada), the product Projet 830 NP and the product Cyanine Infrared Absorbing Dye sold by the company Zeneca Specialties (Manchester, England). For convenience, Cyanine Infrared Absorbing Dye will be referred to hereinbelow by the abbreviation xe2x80x9cZxe2x80x9d.
A particularly advantageous family of absorbers is that characterized by the following skeleton: 
in which X, Y, Z, R, Rxe2x80x2 and Rxe2x80x3 can have many meanings. Typical examples of these meanings are: simple or fused heterocyclic ring for X, simple or fused heterocyclic ring for Z and Y together with the carbon atom to which they are attached, hydrogen, C1-3 alkyl, SO3xe2x88x92 or COOxe2x88x92 for R and Rxe2x80x2 independently of each other, and H or Cl for Rxe2x80x3. Specific examples of the said heterocyclic rings are: 
The presumed structures of certain specific absorbers are: KF 646 
The term xe2x80x9cIR radiationxe2x80x9d is understood to refer to radiation with a wavelength greater than 780 nm.
A typical example of a device used to generate IR radiation is a laser diode which emits at about 830 nm.
The term xe2x80x9cUV radiationxe2x80x9d is understood to refer to radiation with a wavelength of about 10 and about 400 nm.
A typical example of a device used to emit UV radiation is a carbon arc lamp, a mercury vapour lamp, a fluorescent lamp, a tungsten filament lamp, a photographic lamp and a 5000 W actinic-light lamp, which emit in the region 350 and 400 nm.
The term xe2x80x9cdyexe2x80x9d is understood to refer to a coloured compound or preparation capable of tinting the photosensitive composition in order to reveal the image after exposure to light and/or after developing.
Typical examples of dyes are Basonyl blue 636 (Colour Index 42595) from the company BASF (Germany) and Sudan Yellow 150 (Colour Index 11021) from the company BASF (Germany) or mixtures thereof.
The term xe2x80x9ctriazinexe2x80x9d is understood to refer to the family to which the following compounds belong: 2-(1-naphthyl)-4,6-bis(trichloromethyl)-s-triazine, 2-(4-methoxy-1-naphthyl)-4,6-bis(trichloromethyl)-s-triazine, 2-(4-ethoxy-1-naphthyl)-4,6-bis(trichloromethyl)-s-triazine, 2-(4-butoxy-1-naphthyl)-4,6-bis(trichloromethyl)-s-triazine, 2-[4-(2-methoxyethyl)-1-naphthyl]-4,6-bis(trichloromethyl)-s-triazine, 2-[4-(2-ethoxyethyl)-1-naphthyl]-4,6-bis(trichloromethyl)-s-triazine, 2-[4-(2-butoxyethyl)-1-naphthyl]-4,6-bis(trichloromethyl)-s-triazine, 2-(2-methoxy-naphthyl)-4,6-bis(trichloromethyl)-s-triazine, 2-(6-methoxy-5-methyl-2-naphthyl)-4,6-bis(trichloromethyl)-s-triazine, 2-(6-methoxy-2-naphthyl)-4,6-bis(trichloromethyl)-s-triazine, 2-(5-methoxy-1-naphthyl)-4,6-bis(trichloromethyl)-s-triazine, 2-(4,7-dimethoxy-1-naphthyl)-4,6-bis(trichloromethyl)-s-triazine, 2-(6-methoxy-2-naphthyl)-4,6-bis-(trichloromethyl)-s-triazine, 2-(4,5-dimethoxy-1-naphthyl)-4,6-bis(trichloromethyl)-s-triazine, 2-(5-acenaphthyl)-4,6-bis(trichloromethyl)-s-triazine, 2-(2-naphthyl)-4,6-bis (trichloromethyl)-s-triazine, 2-(9-phenanthryl)-4,6-bis(trichloromethyl)-s-triazine, 2-(2-dibenzothienyl)-4,6-bis(trichloromethyl)-s-triazine, 2-(3-benzopyranyl)-4,6-bis(trichloromethyl)-s-triazine, 2-(4-alkoxy-1-anthracyl)-4,6-bis(trichloromethyl)-s-triazine, 2-methyl-4,6-bis(trichloromethyl)-s-triazine, 2-(4-methoxy-styryl)-4,6-bis(trichloromethyl)-s-triazine, 2-(2,3methylenedioxybenzyl)-4,6-bis(trichloromethyl)-s-triazine and (4-methoxy-phenyl)-4,6-bis(trichloromethyl)-s-triazine.
A composition has now been found which gives (i) good results during alkaline developing, irrespective of the system (UV or IR) used to imprint it, (ii) an image which, after developing, has good resistance to the solvents used in printing processes, in particular to isopropyl alcohol, and a lithographic plate comprising the said composition having the abovementioned characteristics.
A first subject of the present invention is therefore a photosensitive composition, characterized in that it comprises
(a) a diazo resin,
(b) a diazo ester,
(c) at least one novolac resin,
(d) an IR ray absorber, and is sensitive to both IR radiation and UV radiation.
A second subject of the present invention is a lithographic plate comprising a support coated with a photosensitive composition, characterized in that
(1) the said composition comprises
(a) a diazo resin,
(b) a diazo ester,
(c) at least one novolac resin,
(d) an IR ray absorber, and in that
(2) the said composition is sensitive to both IR radiation and UV radiation.
Typically, the IR radiation has a wavelength greater than 780 nm, and even more typically it has a wavelength of about 830 nm.
Typically, the UV radiation has a wavelength of about 10 and about 400 nm, and even more typically has a wavelength of 350 and 400 nm.
Preferably, the diazo resin is the product of esterification of a 2,1-naphthoquinonediazidesulphonyl chloride with a product of polycondensation of phenol and/or homologues thereof.
Typically, the diazo resin is the product of esterification of:
2,1-naphthoquinonediazide-4-sulphonyl chloride with a product of polycondensation of phenol or homologues thereof such as, for example, m-cresol and symmetric xylenol. Preferred examples of such commercial diazo resins are chosen from the group comprising the products RO 874 (nitrogen content=1.6% by weight) and RO 849 (nitrogen content=1.9% by weight) from the company Rohner and A 938 (nitrogen content=2.8% by weight) from the company Materiali Sensibili, and/or
2,1-naphthoquinonediazide-5-sulphonyl chloride with a product of polycondensation of phenol or homologues thereof such as, for example, m-cresol and symmetric xylenol. Preferred examples of such commercial diazo resins are chosen from the group comprising the products PW 1160 (nitrogen content=2.4% by weight) and PW 1161 (nitrogen content=3.2% by weight) from the company Clariant and DRS 25 (nitrogen content=2.4% by weight) from the company Materiali Sensibili.
Typically, the diazo resin of the present invention has a weight-average molecular weight of from 3000 to 15,000, preferably of from 5000 to 12,000.
Generally, the composition of the invention may also contain a mixture of diazo resins.
Preferably, the nitrogen content of said diazo resin is of from 1 to 8% by weight. More preferably, said content is of from 1.2 to 3.2% by weight.
Preferably, the diazo ester is a product of partial or total esterification of a tetrahydroxybenzophenone with a 2,1-naphthoquinonediazide sulphonyl chloride.
Typical examples of diazo esters are those obtained by total or partial esterification of a 2,3,4,4xe2x80x2-tetrahydroxybenzophenone or of a 2,2xe2x80x2,4,4xe2x80x2-tetrahydroxybenzophenone with 2,1-naphthoquinonediazide-4-sulphonyl chloride or those obtained by total or partial esterification of a 2,3,4,4xe2x80x2-tetrahydroxybenzophenone or of a 2,2xe2x80x2,4,4xe2x80x2-tetrahydroxybenzophenone with 2,1-naphthoquinone diazide-5-sulphonyl chloride.
Even more typically, the diazo ester is the product obtained by total or partial esterification of 2,2xe2x80x2,4,4xe2x80x2-tetrahydroxybenzophenone with 2,1naphthoquinonediazide-4-sulphonyl chloride giving a mixture of mono-, di-, tri- and tetraester of 2,2xe2x80x2,4,4xe2x80x2-tetrahydroxybenzophenone, sold under the name SDBZ by the company Materiali Sensibili.
Typically, SDBZ contains from 5 to 20% of monoester, from 40 to 60% of diester, from 20 to 40% of triester and from 1 to 10% of tetraester of 2,2xe2x80x2,4,4xe2x80x2-tetrahydroxybenzophenone.
Typically, the nitrogen content of the diazo ester is of from 5 to 13% by weight. Preferably, said content is of from 6 to 9% by weight.
Preferably, the composition of the present invention comprises two novolac resins in which the first novolac resin has a weight-average molecular weight of from 2000 to 6000, while the second has a weight-average molecular weight of from 7000 to 14,000. Even more preferably, the first has a weight-average molecular weight of from 3000 to 5000 and the second has a weight-average molecular weight of from 8000 to 10,000.
Typical examples of suitable commercial novolacs are the high weight-average molecular weight novolac resins such as LB 6564 (weight-average molecular weight=6000-10,000) and LB 744 (weight-average molecular weight=8000-13,000) from the company Bakelite, R 7100 (weight-average molecular weight=9500-10,500) from the company Rohner, and PN 430 (weight-average molecular weight=5000-9500) from the company Clariant and the low weight-average molecular weight novolac resin PN 320 (weight-average molecular weight=3000-5000).
Preferably, the novolac resin according to the present invention is a mixture of at least one high weight-average molecular weight and at least one low weight-average molecular novolac resin. More preferably, the high weight-average molecular weight novolac resin is of about 30-40% by weight in the entire photosensitive composition.
Typically, the novolac resin of the present invention have a softening temperature of from 75 to 135xc2x0 C. Even more typically, the softening temperature of the low weight-average molecular weight novolac resin is of from 75 to 90xc2x0 C. and the softening temperature of the high weight-average molecular weight novolac resin is of from 125 to 140xc2x0 C.
Preferred examples of absorbers are the compounds chosen from the group comprising the commercial products KF 646, KF 645, KF 810, KF 1003, KF 1002, IR HBB 812 and KF 818 from the company Riedel-de-Haen/Allied Signal, the commercial products ADS 805PI, ADS805PP, ADS805PA, ADS805PF, ADS812MI, ADS812MI, ADS815EI, ADS818HI, ADS818HT, ADS822MT, ADS830AT, ADS 830A and ADS838MT from the company American Dye Source, the commercial product Projet 830 NP and the commercial product Cyanine Infrared Absorbing dye from the company Zeneca Specialties.
Preferably, the lithographic plate of the present invention is of positive type.
The composition of the present invention can also comprise a dye.
Preferred examples of dyes are Basonyl Blue 636 (Colour Index 42595) from the company BASF and Sudan Yellow 150 (Colour Index 11021) from the company BASF, and mixtures thereof.
Preferably, the composition of the present invention can also comprise a triazine. Even more preferably, it comprises a triazine substituted with 2 haloalkyl groups.
Typical examples of triazines are 2-(1-naphthyl)-4,6-bis(trichloromethyl)-s-triazine, 2-(4-methoxy-1-naphthyl)-4,6-bis(trichloromethyl)-s-triazine, 2-(4-ethoxy-1-naphthyl)-4,6-bis(trichloromethyl)-s-triazine, 2-(4-butoxy-1-naphthyl)-4,6-bis(trichloromethyl)-s-triazine, 2-[4-(2-methoxyethyl)-1-naphthyl]-4,6-bis(trichloromethyl)-s-triazine, 2-[4-(2-ethoxyethyl)-1-naphthyl]-4,6-bis(trichloromethyl)-s-triazine, 2-[4-(2-butoxyethyl)-1-naphthyl]-4,6-bis(trichloromethyl)-s-triazine, 2-(2-methoxy-1-naphthyl)-4,6-bis(trichloromethyl)-s-triazine, 2-(6-methoxy-5-methyl-2-naphthyl)-4,6-bis(trichloromethyl)-s-triazine, 2-(6-methoxy-2-naphthyl)-4,6-bis(trichloromethyl)-s-triazine, 2-(5-methoxy-1-naphthyl)-4,6-bis(trichloromethyl)-s-triazine, 2-(4,7-dimethoxy-1-naphthyl)-4,6-bis(trichloromethyl)-s-triazine, 2-(6-methoxy-2-naphthyl)-4,6-bis(trichloromethyl)-s-triazine, 2-(4,5-dimethoxy-1-naphthyl)-4,6-bis(trichloromethyl)-s-triazine, 2-(5-acenaphthyl)-4,6-bis(trichloromethyl)-s-triazine, 2-(2-naphthyl)-4,6-bis(trichloromethyl)-s-triazine, 2-(9-phenanthryl)-4,6-bis(trichloromethyl)-s-triazine, 2-(2-dibenzothienyl)-4,6-bis(trichloromethyl)-s-triazine, 2-(3-benzopyranyl)-4,6-bis(trichloromethyl)-s-triazine, 2-(4-alkoxy-1-anthracyl)-4,6-bis(trichloro-methyl)-s-triazine, 2-methyl-4,6-bis(trichloromethyl)-s-triazine, 2-(4-methoxystyryl)-4,6-bis(trichloromethyl)-s-triazine, 2-(2,3-methylenedioxybenzyl)-4,6-bis(trichloromethyl)-s-triazine and 2-(4-methoxyphenyl)-4,6-bis(trichloromethyl)-s-triazine.
Even more preferably, the triazine is 2-(4-methoxy-1-naphthyl)-4,6-bis(trichloromethyl)-s-triazine sold by the company Clariant under the reference code BU 1557.